Compensating arrangement for television tubes



March 2.9, 1945..

u. KNICK 2,371,897

COMPENSATING ARRANGEMENT FOR TELEVISION TUBES GENERATOR Filed NOV. 12, 1941 SOURCE OF 4TELEVISION SXG'NALS souRcE TELEVISION SIGNALS INVENTOR ATTORNEY Patented Mar. 20, 1945 UNITED STATES COMPENSATING ARRANGEMENT FOR.

THEVISION TUBES Ulrich Knick, Berlin-Zehlendor f- West, Germany; vested in the Alien Property Custodian Application November 12, 1941, Serial No. 418,762

In Germany September 5, 1940 3 Claims.

The present invention relates to arrangements for operating Braun tubes and has special reference to devices for compensating the fluctuations in anode voltage caused by the luminosity control of television tubes.

In television tubes the anode voltage, which mostly amounts to several thousands of volts, is usually taken from a transformer and, then, rectified and smoothed out by filtering means. It is well known, that such power supply systems will not give a constant voltage at the varying loads caused by the changes occurring in the subjectmatter of the picture to be transmitted.

It was tried to neutralize these disturbing voltage fluctuations by the use of considerably bigger power supply systems, that is by connecting, in parallel to the television tubes, a constant resistor, through which is flowing a current considerably larger than that flowing through the television tube. It is true that, owing to this constant and continuous current, the fluctuation percentage of the current taken from the p wer supply system is rendered considerably smaller, but this procedure, let alone the high expenditure, ensures also very high losses in the parallel resistor, which in many cases renders impossible the use of said procedure. Moreover, it has been proposed to have a parallel D. C. connection of the television tube and a compensating tube, the

latter being controlled in phase opposition with tion of the compensating tube, since a special type of compensating tube must be made for each type of television tubes and since, owing to the disparity of technical data occurring in single piece manufacture, only very few out of a great number of compensating tubes will possess the characteristic curve required for compensation.

Further it has been proposed to connect, in

parallel with the television tube, a compensating tube which has a constant grid biasing value and is controlled by the fluctuations occurring in the anode voltage. By this method a decrease in the anode voltage fluctuations may, in fact, be obtained in a very simple way, but such decrease may be efiected only, since a fluctuation in anode voltage is required for anode control of the compensating tube and a residual fluctuation of voltage will always remain. Therefore this procedure may not be employed in those cases where the 2B trol grid of the auxiliary tube.

requirements made upon the constancy of the anode voltage are more severe.

It is an object ,of the invention to combine a television tube, the corresponding power supply system, and a compensating tube in such a way that the above mentioned disadvantages will not make themselves felt and, therefore, the current taken from the power supply system will, at minimum expenditure, be held upon a value independent from the anode current of the television tube.

In accordance with the invention and in order to produce a high constant voltage, practically independent of anode fluctuations, for operating .television tubes, there is connected, between the go connected a resistor R, which, at the same time,

is situated in the grid-control circuit of the auxiliary tube. That end of the resistor which, in its direction, is away from the cathode of the television tube will be directed towards the con- It is of advantags to choose the resistor R such, that the arithmetical product of the slope of the auxiliary tube and of R, measured in ohms, is bigger than 1 In the drawing, Figs. 1 and 2 show schematically two illustrative embodiments of the invention.

In Fig. 1, the current, supplied by generator l and having the intensityIges, is led, by way of line 2, on the one hand, to the anode of television tube 3, and, on the other hand, to the anode of auxiliary tube J3, the internal resistance of which will, subsequently, be indicated by R1 and the slope of which by S. Into the cathode cir cult ofthe television tube is inserted a resistor R, which is so connected with the cathode of auxiliary tube t, that it is traversed by the anode voltage of the television tube as well as the anode voltage of the compensating tube. The

5 modulation voltages are led in by way of terminals 5 and 6 and conducted to the Wehnelz. cylinder, provided with the leak resistor 8 of the television tube. For this reason the electron stream of the television tube is modulated as a function of the actually existing picture luminosity, and the voltage drop' at resistor R will, therefore, also fluctuate in the same rhythm. At this resistor R, however, is produced the grid biasing potential for controlling grid 9 of tube 4 and, therefore, auxiliary tube 4 is controlled in the same rhythm as the television tube, but with opposite polarity.

Resistor R is in parallel with the apparent internal cathode resistance 01 tube 4, which is equal to the reciprocal value of the slope of this tube. Thus the voltage drop resulting at resistor R is kept practically constant, the constancy being the better, the smaller the apparent cathode resistance (the steeper the slope) with respect to resistor R. The constant potential at resistor R will produce a constant current, flowing through this resistor, this current being, at the same time, the total current which is taken from the generator.

Resistor R. is bridged, as regards A. C., by a condenser C, and thereby it is obtained that the rapidly succeeding changes in luminosity, that is the so-called A. C. component of picture modulation, is led directly to the grid cathode space of the television tube, a substantial portion of the signal voltage put in would, possibly, be consumed in resistor R, without an eifect.

If an impulse of e. g..positive polarity is, by way of terminal 5, fed into the controlling grid the television tube, anode current I1 of the television tube will increase by the amount A11,

and at cathode resistor R there will arise an addltional voltage drop R-Ah. But as the voltage drop at resistor R is decisive of the potential of controlling grid 9 of the auxiliary tube, said potential will be more negative by the amount R-Ah and. the slope of the auxiliary tube being S, anode current I is decreased by the amount S-R-Alr. By a convenient selection of R and 8 it will be feasible to compensate the increase in anode current I1 by a decrease in anode current I in such a way that the total current (lm=l+li) will, practically, be constant.

By the above-described combination of current supply system I and auxiliary tube 4 there will be achieved an efiect as if the apparent internal resistance R'gen of the current supply system, feeding the television tube, had come to be wherein R1 indicates the internal resistance of the auxiliary tube and R the inner resistance of the current supply system without auxiliary tube.

In the illustrated circuit arrangement only the changes of the anode D. C. caused by the fluctuations in the average luminosity of the picture-are compensated by the auxiliary tube, while the rapid fluctuations in the anode voltage caused by the different luminosities of the single picture spots, fluctuating around the average luminosity of the picture at a relatively high frequency, are compensated by the filtering means arranged in the anode current supply system. The time constant of R' and condenser C must, however, be smaller than the period of time relating to one line change of the television transmission.

In certain cases it may be convenient to further reduce the required expenditure in filtering means by notonly compensating the fluctuations in average picture luminosity, but also the anode current fluctuations caused by the picture modulation. In this case the condenser, bridging resistor R, must be left out.

The arrangement in accordance with the invention is used, to particular advantage, in combination with television tubes which are controlled in a correct ratio with respect to their luminosities, that is such to which'is fed a varconstantly examined by the viewer or by service people. Such sets are e. g. used for testing the quality of television transmissions, wherein single scans or successions of lines are, at certain periodically recurring times or under the influence of a remote control device, selected from a television transmission and recorded photo-- described wiring and corresponding parts in they two figures bear the same reference numerals. The arriving video signals are led to the control ling electrode of the television tube by way of terminals 5 and 6 and coupling condenser 1. The cathode of a diode I0 is connected to this controlling electrode, the anode of said diode being linked up with tap l3 of resistor R. By means of resistor H, linked up with tap I 2 of resistor R, the diode is under a corresponding biasing potential, whereby the television tube control of correct luminosity is secured in a manner known per se. In certain cases it may be of advantage that suitable devices be provided in 'order to adjust the point of operation of auxiliary tube 4, that is in order to obtain an operation within the range of steepest slope. To this effect the end of resistor R, not directed towards the television tube, is led to the slidable tap of resistor [5, which is so connected to the source of auxiliary voltage I6, that it is traversed by a current. The intensity of this current may, if necessary, be adjusted by changing the control resistor l1, and thereby orby sliding tap H, the grid biasing potential and, therefore, the point of operation of the auxiliary tube is usually adjusted to the most advantageous voltage.

The invention is of particularadvantage in combination with transformer relaxation oscillators, in which the high voltage impulses generated during the feed-back period are rectified and serve for generating high voltage for television tubes, since these devices for obtaining anode voltage have a very high apparent internal resistance, particularly if the constant potential is generated in a multiple stage system.

What I claim is:

1. In combination, a cathode ray tube comprising an anode, cathode and control electrode, a source of potential connected to the anode of said tube, a source of signals connected to the control electrode of said tube and means for compensating the fluctuations in the anode voltage caused by the fluctuations of said signals comprising a grid controlled auxiliary tube connected in parallel with the anode-cathode circuit of said cathode ray tube and a resistor connected between the cathode of said cathode ray tube and said source of potential and also between the cathode of said auxiliary tube and grid of said auxiliary tube.

2. In combination, a cathode ray tube comprising an anode, cathode and control electrode, a source of potential connected to the anode of said tube, a source of signals connected to the control electrode of said tube and means for compensating the fluctuations in the anode voltage caused by the fluctuations of said signals comprising a grid controlled auxiliary tube connected to the anode-cathode circuit of said cathode ray tube and a resistor connected to the cathode of said cathode ray tube and said source of potential and also between the cathode of said auxiliary tube and grid of said auxiliary tube.

3. In apparatus of the character described for compensating the fluctuations in voltage impressed across a cathode ray tube caused by changes in the current flowing through the tube, the combination of, a cathode ray tube having a cathode and an anode and a control electrode, a source of signals connected to said control electrode, a source of current connected between said cathode and said anode, and circuit means connected between said source of current and said cathode and anode for preventing a fluctuation in the voltage across said cathode and anode which would result from a change in the current flowing through said tube due to the action of said control electrode comprising an auxiliary tube having an anode connected to the anode of the cathode ray tube and a cathode connected to the cathode of the cathode ray tube, a resistor connected between said cathodes and the source of current, and a control electrode in said auxiliary tube to control the flow of current therethrough and connected to said source of current between the source and said resistor.

ULRICH CK. 

